The paper explores the capability of the advanced Pastor-Zienkiewicz constitutive model to accurate simulate the deformability, the shear strength and the static liquefaction of an air-fall volcanic (pyroclastic) soil, which was involved in catastrophic landslides of the flow type. The calibration and validation of two distinct versions of the PZ constitutive model is done for both undisturbed (loose) and remoulded (dense) saturated specimens. Either drained or undrained triaxial tests are properly reproduced through the model. The potentialities deriving from the use of an advanced constitutive model are pointed out.